The invention is directed to an apparatus adapted to be used for the automatic transfer of sheets from which leaflets are formed from a printing press to a folder.
Leaflets may be formed by printing a paper web with printed subject matter, separating the web into individual sheets, transferring the individual sheets to a folder, and then folding the individual sheets into leaflets. As disclosed in U.S. Pat. No. 4,616,815 to Michael Vijuk, printed and cut shingled sheets were previously transferred manually from a web printing press to an automatic folding machine used for folding the sheets to form leaflets. The invention disclosed in that Vijuk patent is advantageous in that allows the previously manual transfer of sheets to be automated, which is particularly advantageous in view of the relatively high output of sheets from a web printing press, which may be on the order of 40,000 sheets per hour or more.
As shown in FIG. 1, the Vijuk patent discloses a printing press 15 which applies printed subject matter to a paper web and cuts the paper web into individual sheets to generate a shingled stream of sheets. The sheets are conveyed by a sheet transfer conveyor 16 to a stacking station 18 where sheets may accumulate in a vertical stack. Sheets are periodically removed from the bottom of the stack of sheets at the stacking station 18 by a rotatable vacuum cylinder 40 (shown in FIG. 6) and transferred to an alignment conveyor 22 for subsequent transfer to a folding station 14.
A prior art apparatus for automatically transferring sheets from a web printer to a folding machine generally in accordance with the disclosure of the Vijuk patent controlled the vacuum cylinder so that its rotational speed varied in response to the height of the stack of sheets in the stacking station, with the height of the stack of sheets being detected by a sensor positioned adjacent the stack. The prior art apparatus also included a sensor for sensing whether the height of the stack of sheets was below a minimum height. In that case, a visual message would be displayed to prompt the operator to place additional sheets in the stack at the stacking station. The prior art apparatus also controlled when a vacuum was provided to the interior of the vacuum cylinder was selectively opening and closing a pneumatic valve that fluidly coupled the vacuum cylinder to a vacuum pump.
The prior art apparatus described above included a batch control module that allowed the operator to input a desired number of sheets which was to be transferred as a batch, along with a desired time delay between batches of sheets. The prior art apparatus also included a rate control module that allowed the operator to input a desired distance or gap between adjacent sheets as they are fed by the vacuum cylinder, as well as the time duration for which the pneumatic valve was opened and closed. Based upon those parameters entered by the operator, the batch control module and rate control module controlled the time periods when the pneumatic valve was on and off, and thus the removal of the sheets from the stack by the vacuum cylinder.